DESCRIPTION (Adapted from applicant's description): This proposal uses a combination of biochemical and x-ray crystallographic approaches to study the structural basis of aberrant RNA processing in genetic disease. CUG-binding protein (CUG-BP), ELAV-type RNA-binding protein (ETR) -1 and -3 are proteins responsible for developmentally regulated splice site selection in a variety of tissues and cell types. These proteins contain 3 copies of the RNA recognition motif (RRM) and participate in a wide range of RNA processing events including, splicing, transport and mRNA turnover. CUG-BP, ETR-1 and ETR-3 specifically effect splice site selection in striated muscle tissue. CUG-BP was first isolated in connection with myotonic dystrophy (DM), a genetic disease that results from an expansion of CUG repeats in an untranslated region of the myotonin kinase gene and results in symptoms from mild myotonia to severe retardation at birth. DM is an unfortunately common disease (1 in 8000 births). CUG-BP also interacts with CUG-rich sequences found in a number of other mRNAs. Alteration of in vivo levels of CUG-BP, ETR- 1 or ETR-3 result in tissue specific changes in splicing that appear to mimic either developmental or disease related RNA processing defects. This award would be used to examine how RNA sequences already involved in ribonucleoprotein complexes are read or "scanned" by other RNA binding proteins such as those involved in alternate splicing. Crystallographic conditions required to determine the three-dimensional structure of CUG-BP, ETR-1, and ETR-3 bound to their physiologically relevant RNA targets using x- ray crystallography will also be determined. The results derived from this proposal will significantly broaden our understanding of how aberrant RNA splicing occurs and address fundamental aspects of RNA metabolism to provide immediate insights to investigators working in the field of human disease pathogenesis.